About 40 tests are crashing in debug builds with the same trace. For example: WebKitBuild/WPE/Debug/bin/TestWebKitAPI/WPE/TestConsoleMessage /webkit/WebKitConsoleMessage/js-exception This issue happens when running together with other test cases, as running the test (function, not the program) isolated it works. Trace: ASSERTION FAILED: !m_deletionHasBegun DerivedSources/ForwardingHeaders/wtf/ThreadSafeRefCounted.h(58) : void WTF::ThreadSafeRefCountedBase::ref() const 1 0x557660b7f47f WTFCrash 2 0x557660b7f495 WTFIsDebuggerAttached 3 0x55765f2274ce WTF::ThreadSafeRefCountedBase::ref() const 4 0x7fae2fc545f2 WTF::DefaultRefDerefTraits<WebKit::WebProcessPool>::refIfNotNull(WebKit::WebProcessPool*) 5 0x7fae2fc491bb WTF::RefPtr<WebKit::WebProcessPool, WTF::RawPtrTraits<WebKit::WebProcessPool>, WTF::DefaultRefDerefTraits<WebKit::WebProcessPool> >::RefPtr(WebKit::WebProcessPool*) 6 0x7fae2fc3c979 WTF::RefPtr<WebKit::WebProcessPool, WTF::RawPtrTraits<WebKit::WebProcessPool>, WTF::DefaultRefDerefTraits<WebKit::WebProcessPool> >::operator=(WebKit::WebProcessPool*) 7 0x7fae2fc2db2e WebKit::WebProcessProxy::WeakOrStrongPtr<WebKit::WebProcessPool>::updateStrongReference() 8 0x7fae2fc1dfdc WebKit::WebProcessProxy::WeakOrStrongPtr<WebKit::WebProcessPool>::setIsWeak(WebKit::WebProcessProxy::IsWeak) 9 0x7fae2fbec6b8 WebKit::WebProcessProxy::setIsInProcessCache(bool) 10 0x7fae2fbe07c8 WebKit::WebProcessCache::CachedProcess::~CachedProcess() 11 0x7fae2fc23f14 std::default_delete<WebKit::WebProcessCache::CachedProcess>::operator()(WebKit::WebProcessCache::CachedProcess*) const 12 0x7fae2fc141dc std::unique_ptr<WebKit::WebProcessCache::CachedProcess, std::default_delete<WebKit::WebProcessCache::CachedProcess> >::~unique_ptr() 13 0x7fae2fc23cbe WTF::KeyValuePair<WebCore::RegistrableDomain, std::unique_ptr<WebKit::WebProcessCache::CachedProcess, std::default_delete<WebKit::WebProcessCache::CachedProcess> > >::~KeyValuePair() 14 0x7fae2fc23d2c WTF::HashTable<WebCore::RegistrableDomain, WTF::KeyValuePair<WebCore::RegistrableDomain, std::unique_ptr<WebKit::WebProcessCache::CachedProcess, std::default_delete<WebKit::WebProcessCache::CachedProcess> > >, WTF::KeyValuePairKeyExtractor<WTF::KeyValuePair<WebCore::RegistrableDomain, std::unique_ptr<WebKit::WebProcessCache::CachedProcess, std::default_delete<WebKit::WebProcessCache::CachedProcess> > > >, WTF::DefaultHash<WebCore::RegistrableDomain>, WTF::HashMap<WebCore::RegistrableDomain, std::unique_ptr<WebKit::WebProcessCache::CachedProcess, std::default_delete<WebKit::WebProcessCache::CachedProcess> >, WTF::DefaultHash<WebCore::RegistrableDomain>, WTF::HashTraits<WebCore::RegistrableDomain>, WTF::HashTraits<std::unique_ptr<WebKit::WebProcessCache::CachedProcess, std::default_delete<WebKit::WebProcessCache::CachedProcess> > > >::KeyValuePairTraits, WTF::HashTraits<WebCore::RegistrableDomain> >::deallocateTable(WTF::KeyValuePair<WebCore::RegistrableDomain, std::unique_ptr<WebKit::WebProcessCache::CachedProcess, std::default_delete<WebKit::WebProcessCache::CachedProcess> > >*) 15 0x7fae2fc24d50 WTF::HashTable<WebCore::RegistrableDomain, WTF::KeyValuePair<WebCore::RegistrableDomain, std::unique_ptr<WebKit::WebProcessCache::CachedProcess, std::default_delete<WebKit::WebProcessCache::CachedProcess> > >, WTF::KeyValuePairKeyExtractor<WTF::KeyValuePair<WebCore::RegistrableDomain, std::unique_ptr<WebKit::WebProcessCache::CachedProcess, std::default_delete<WebKit::WebProcessCache::CachedProcess> > > >, WTF::DefaultHash<WebCore::RegistrableDomain>, WTF::HashMap<WebCore::RegistrableDomain, std::unique_ptr<WebKit::WebProcessCache::CachedProcess, std::default_delete<WebKit::WebProcessCache::CachedProcess> >, WTF::DefaultHash<WebCore::RegistrableDomain>, WTF::HashTraits<WebCore::RegistrableDomain>, WTF::HashTraits<std::unique_ptr<WebKit::WebProcessCache::CachedProcess, std::default_delete<WebKit::WebProcessCache::CachedProcess> > > >::KeyValuePairTraits, WTF::HashTraits<WebCore::RegistrableDomain> >::clear() 16 0x7fae2fc14b18 WTF::HashMap<WebCore::RegistrableDomain, std::unique_ptr<WebKit::WebProcessCache::CachedProcess, std::default_delete<WebKit::WebProcessCache::CachedProcess> >, WTF::DefaultHash<WebCore::RegistrableDomain>, WTF::HashTraits<WebCore::RegistrableDomain>, WTF::HashTraits<std::unique_ptr<WebKit::WebProcessCache::CachedProcess, std::default_delete<WebKit::WebProcessCache::CachedProcess> > > >::clear() 17 0x7fae2fbdfb33 WebKit::WebProcessCache::clear() 18 0x7fae2fbe1ca7 WebKit::WebProcessPool::~WebProcessPool() 19 0x7fae2fbe2352 WebKit::WebProcessPool::~WebProcessPool() 20 0x7fae2ee20c06 WTF::ThreadSafeRefCounted<API::Object, (WTF::DestructionThread)0>::deref() const::{lambda()#1}::operator()() const 21 0x7fae2ee20c4d WTF::ThreadSafeRefCounted<API::Object, (WTF::DestructionThread)0>::deref() const 22 0x7fae2f252e24 WTF::Ref<WebKit::WebProcessPool, WTF::RawPtrTraits<WebKit::WebProcessPool> >::~Ref() 23 0x7fae2fbde9aa /app/webkit/WebKitBuild/Debug/lib/libWPEWebKit-1.0.so.3(+0x104d19aa) [0x7fae2fbde9aa] 24 0x7fae2fc0266a /app/webkit/WebKitBuild/Debug/lib/libWPEWebKit-1.0.so.3(+0x104f566a) [0x7fae2fc0266a] 25 0x7fae2fc02692 /app/webkit/WebKitBuild/Debug/lib/libWPEWebKit-1.0.so.3(+0x104f5692) [0x7fae2fc02692] 26 0x7fae2ee84144 std::default_delete<WTF::Detail::CallableWrapperBase<void, bool> >::operator()(WTF::Detail::CallableWrapperBase<void, bool>*) const 27 0x7fae2ee834a2 std::unique_ptr<WTF::Detail::CallableWrapperBase<void, bool>, std::default_delete<WTF::Detail::CallableWrapperBase<void, bool> > >::~unique_ptr() 28 0x7fae2ee82a00 WTF::Function<void (bool)>::~Function() 29 0x7fae2f4549d8 WTF::CompletionHandler<void (bool)>::operator()(bool) 30 0x7fae2fbf2f71 WebKit::WebProcessProxy::didReceiveMainThreadPing() 31 0x7fae2f258109 void IPC::callMemberFunctionImpl<WebKit::WebProcessProxy, void (WebKit::WebProcessProxy::*)(), std::tuple<>>(WebKit::WebProcessProxy*, void (WebKit::WebProcessProxy::*)(),